As a metal mold structure for casting two cylinder blocks at a time there is known the structure, as disclosed in patent reference 1, that a slide core provided between the cylinder blocks is operated by an inclined pin provided in a fixed mold. Further, as disclosed in patent reference 2, there is known the structure that a slide core is operated by a cylinder device.    Patent reference 1: Japanese patent laid-open publication No. S61-95741.    Patent reference 2: Japanese patent laid-open publication No. 2007-152382.